In spite of abundant existing Literature in this research field, it is not possible to affirm that there is a unique theoretical frame for the analysis of the internationalization process.The objective of this paper is analyze empirical works, published between 1999 and 2004, centered specifically in the internationalization of the SME'S, in order to identify key empirical findings and propose future research lines. We analyzed the content of the studies from six different approaches: (1) the Phases, Processes and Life cycle of the SME's that are internationalized theoretical approach, (2) the Networks and Relations approach, (3) the Strategic approach, (4) the Resources, Knowledge and Information approach, (5) the Culture and Multinational approach (6) the Foreign Direct Investment and Economic Growth approach.